This invention relates generally to the production of olefins and, more particularly, to the production of light olefins via processing of dimethyl ether.
A major portion of the worldwide petrochemical industry is concerned with the production of light olefin materials and their subsequent use in the production of numerous important chemical products such as via polymerization, oligomerization, alkylation and the like well-known chemical reactions. Light olefins generally include ethylene, propylene and mixtures thereof. These light olefins are essential building blocks used in the modem petrochemical and chemical industries. A major source for light olefins in present day refining is the steam cracking of petroleum feeds. For various reasons including geographical, economic, political and diminished supply considerations, the art has long sought sources other than petroleum for the massive quantities of raw materials that are needed to supply the demand for these light olefin materials.
The search for alternative materials for light olefin production has led to the use of oxygenates such as alcohols and, more particularly, to the use of methanol, ethanol, and higher alcohols or their derivatives such as dimethyl ether, diethyl ether, etc., for example. Molecular sieves such as microporous crystalline zeolite and non-zeolitic catalysts, particularly silicoaluminophosphates (SAPO), are known to promote the conversion of oxygenates to hydrocarbon mixtures, particularly hydrocarbon mixtures composed largely of light olefins.
Such processing, wherein the oxygenate-containing feed is primarily methanol or a methanol-water combination (including crude methanol), typically results in the release of significant quantities of water upon the sought conversion of such feeds to light olefins. For example, such processing normally involves the release of about 2 mols of water per mol of ethylene formed and the release of about 3 mols of water per mol of propylene formed. The presence of such increased relative amounts of water can significantly increase the potential for hydrothermal damage to the oxygenate conversion catalyst. Moreover, the presence of such increased relative amounts of water significantly increases the volumetric flow rate of the reactor effluent, resulting in the need for larger sized vessels and associated processing and operating equipment, including necessitating higher compression requirements.
U.S. Pat. No. 5,714,662 to Vora et al., the disclosure of which is hereby incorporated by reference in its entirety, discloses a process for the production of light olefins from a hydrocarbon gas stream by a combination of reforming, oxygenate production, and oxygenate conversion wherein a crude methanol stream (produced in the production of oxygenates and comprising methanol, light ends, and heavier alcohols) is passed directly to an oxygenate conversion zone for the production of light olefins.
While such processing has proven to be effective for light olefin production, further improvements have been desired and sought. For example, there is an ongoing desire and need for reducing the size and consequently the cost of required reaction vessels. Further, there is an ongoing desire and need for processing schemes and arrangements that can more readily handle and manage the heat of reaction and byproduct water associated with such processing.